Petroleum fluids are often transported from one location to another through pipelines. Usually more than one fluid is moved through a single pipeline, for example, gasolines of various grades, kerosene, jet fuel, and diesel fuel, may all be moved through a single pipeline in any order or sequence. The gasolines transported through pipelines may be either regular gasoline, unleaded, or super unleaded. When two fluids are transferred through a pipeline in sequence, there is usually mixing at the interface of the two fluids so that each fluid contaminates the other. When pipelining of the fluids is completed, this contaminated material must be separated to keep the individual products in specification.
The operator of the pipeline must know at all times what product is flowing through the pipeline at any given location so that he can carry out appropriate switching to be sure that products are placed in correct storage or directed to the correct terminals.
Identification of liquids flowing through a pipeline is made by pulling samples periodically. Since only a few products are handled in the pipeline, usually from two to five products, it is easy to identify each particular product by a gravity measurement. Gravity is customarily determined by a hydrometer. The mixed material at the interface between two liquids may also be identified by gravity and color. The operator is also concerned with cleanliness of the flowing liquids and whether or not the liquids contain any solids. All of the above information may readily be obtained by visual examination of the liquid samples.
Environmental concerns dictate that personnel drawing samples from a pipeline not be exposed to dangerous chemicals. Among such chemicals is benzene which is often present in small amounts in gasolines, which are a primary pipeline petroleum product.
It is of great importance to provide a sampling system which is vapor tight and which provides the necessary means for visual evaluation of pipeline petroleum liquids.